The invention is directed to a process for the production of aqueous sodium methioninate solutions having a low content of sodium carbonate from the crude hydrolysis mixtures resulting from the saponification of 5-(.beta.-methylmercaptoethyl)-hydantoin with 1.1 to 6 equivalents of sodium hydroxide and/or sodium carbonate.
The essential aminoacid methionine for a long time, to a considerable extent has been produced synthetically and used as a feed additive, especially in industrially produced mixed feeds for birds, swine, and other agriculturally useful animals. However, problems occur in storing and processing the methionine. From the very beginning methionine present in crystalline form is not pourable and can cake during storage if this is not avoided through suitable expensive crystallization conditions. If the methionine is present in powder form, in a given case with an addition of an additive preserving pourability, then there exists the problems of dust formation occurring in the handling of all powdery materials.
A further point is the exact dosaging and homogeneous distribution of solid methionine in mixed feed. In the supplementation of mixed feeds with methionine there are used low concentrations of the order of magnitude of about 0.01 to 1.0 weight percent. In order to guarantee a homogeneous distribution, there is unavoidable the production of a special premixture containing methionine in correspondingly higher concentration.
In place of solid methionine in more advantageous manner there can be employed a liguid formulation. Liquids can be dosed exactly and homogeneously mixed with other components of the mixture present in the desired concentrations by spraying.
Since free methionine is only slightly soluble in water, there are better suited for the requirements of practice salts having good water solubility, especially sodium methioninate. Now there are indeed necessarily formed aqueous solutions of sodium methioninate of necessity if there is saponified an aqueous solution of 5-(.beta.-methylmercaptoethyl)hydantoin with 1.1 to 6 equivalents of sodium hydroxide and/or sodium carbonate in a known and frequently used process for the production of DL-methionine. This crude hydrolysis mixture, however, likewise necessarily contains also a more or less large amount of sodium carbonate, in general at least one half to one mole per mole of sodium methioninate. This sodium carbonate is undesired as a foreign salt in the production of mixed feed.
Furthermore, moreover, it is inclined to partially crystallize out in long storage so that the crude hydrolysis mixtures are not storage stable. It would naturally be possible without further to isolate the methionine from the crude hydrolysis mixtures in known manner and to then subsequently dissolve the methionine in aqueous sodium hydroxide to a sodium methioninate solution. However, it would be simpler and above all, more favorable cost wise if there could be separated from the crude hydrolysis mixture at least the greatest part of the sodium carbonate contained therein. Previously, however, there was not known a process for the separation of sodium methioninate and sodium carbonate.